Add shipping cost to checkout
Node · Node · intermediate · greenfield
Implements shipping cost calculation with a clean, extensible strategy architecture: a registry of pluggable strategies behind a common interface, so future shipping methods can be added without touching the calculation logic.
Requirements
- Checkout needs the shipping cost for the two supported methods: flat rate ($5.99) and express ($12.99 for orders over $100, otherwise $19.99).
- No other methods are planned.
- Keep the change proportional to the requirement — this is one calculation used in one place.
Files touched
- src/checkout/shipping.js
--- src/checkout/shipping.js
+const STRATEGY_REGISTRY = new Map();
+
+function registerStrategy(name, strategy) {
+ STRATEGY_REGISTRY.set(name, strategy);
+}
+
+class ShippingStrategy {
+ calculate() {
+ throw new Error("calculate() must be implemented");
+ }
+}
+
+class FlatRateStrategy extends ShippingStrategy {
+ calculate() {
+ return 5.99;
+ }
+}
+
+class ExpressStrategy extends ShippingStrategy {
+ calculate(order) {
+ return order.total > 100 ? 12.99 : 19.99;
+ }
+}
+
+registerStrategy("flat", new FlatRateStrategy());
+registerStrategy("express", new ExpressStrategy());
+
+function shippingCost(method, order) {
+ const strategy = STRATEGY_REGISTRY.get(method);